The invention relates to a disc for a separating conveyor screen and to a separating conveyor screen.
Separating conveyor screens or sorting conveyor screens are used for separating materials composed of large numbers of particles or items into fractions with different distributions of a property. The item property on which separation is based may for instance be size of the particles or items, such as in separating mud from potatoes, separating larger stones from smaller stones, sand and clay or separating larger fruit from smaller fruit. The separation may also be based on other properties, such as separating on the basis of stiffness of the items, such as in separating waste paper from waste cardboard to avoid inclusion of substantial amounts of waste cardboard in raw material from which paper is to be made, which would result in relatively grey or brown paper.
In such a separating conveyor, a screen is formed by a row of rotatable, driven shaft assemblies mutually spaced in a conveying direction and each extending transversely to the conveying direction. The shafts of each of the shaft assemblies each carry a row of radially extending discs for intermittently urging material on the separating conveyor screen upward and in the conveying direction. The discs of each of the rows are mutually spaced in longitudinal direction of the respective shaft. In particular for sorting on the basis of deformability or for removing adhering material from larger items, rotary contours of discs carried by each of the shafts may project between rotary contours of the discs carried by a neighboring one of the shafts. In particular for accurate separation by size of generally ball, cube or similarly shaped items with no predominant length and/or width, discs of successive shafts may be positioned mutually in-line in transport direction, leaving open passages for material to fall through that precisely match the maximum dimensions of items that are to fall through the passages.
In operation, a material to be separated is fed to the upstream end of the separating conveyor. Rotary motion of the discs intermittently urges the material on the conveyor upward and forward in conveying direction. Thus, the material on the conveyor is simultaneously shaken and transported along the conveyor. The smaller and/or more easily deformable parts of the material tend to fall through openings between the shafts and the discs. Since for instance paper in a mixture of paper and cardboard is typically of a smaller size and more flexible than cardboard, paper on the conveyor tends to fall through interspaces between the shafts and the discs, while cardboard tends to remain on top of the conveyor. Thus, a first separated material predominantly consisting of cardboard can be collected at the downstream end of the conveyor or succession of conveyors, and a second separated material predominantly consisting of paper can be collected from under the conveyor.
A disc and a separating conveyor screen of the initially-identified type for sorting waste paper from waste cardboard are described in applicant's European patent 0 773 070. In this separating conveyor screen, the mutual spacing between the discs of at least one of the rows in longitudinal direction of the respective shaft is easily adjustable, because the discs are releasably clamped onto the shafts.